1. Field of the Invention
The present invention relates generally to a liquid crystal display device and, more particularly, to a liquid crystal display device exhibiting a high display performance and a high yield and requiring a small number of steps.
2. Description of the Background Art
A liquid crystal display device generally employed nowadays is constructed such that two glass substrates having electrodes are set in a face-to-face (opposing) relationship, peripheries of these two substrates exclusive of a liquid crystal filling port are fixed by a bonding agent, the liquid crystal is interposed between the two substrates, and the liquid crystal filling port is sealed by a sealing agent. Plastic beads or the like having a uniform particle diameter are dispersed between the substrates as spacers for keeping a fixed distance between these two substrates.
A liquid crystal display device for color display includes color filters R, G and B of color layers that are disposed on one of the two glass substrates. For instance, a color dot matrix liquid crystal display device based on a simple matrix drive includes a Y-substrate having a Y-electrode subjected to band-like patterning in a lateral (Y) direction and an X-substrate having color layers under the X-electrode subjected to the band-like patterning in a vertical (X) direction, wherein the X- and Y-substrates are provided in a face-to-face relationship so that the X-and Y-electrodes are substantially orthogonal to each other, and a liquid crystal material is sealed in therebetween. The liquid crystal display device may involve the use of display systems such as, e.g., TN (Twisted Nematic) type, STN (Super Twisted Nematic) type, GH (Guest Host) type, or ECB (Electrically Controlled Birefringence) type and a dielectric liquid crystal. The sealing agent involves the use of, e.g., a bonding agent of a thermosetting type or an ultraviolet ray hardening acrylic or epoxy group.
Furthermore, the color active matrix drive liquid crystal display device is constructed of a TFT active matrix substrate, i.e., an active matrix substrate with a switching element, e.g., a thin-film transistor (TFT) with a semiconductor layer composed of amorphous silicon (a-Si), and a pixel electrode, a signal electrode and a gate electrode that are connected thereto, and also an opposite substrate disposed in the face-to-face relationship with the TFT active matrix substrate. The color layers R, G and B are disposed on the opposite substrate. Disposed on a screen peripheral portion is a silver paste serving as an electrode transfer member (transfer) for applying a voltage to the opposite substrate from above the active matrix substrate. The two substrates are electrically connected by this electrode transfer member, and the liquid crystal material is sealed in between those two substrates. Furthermore, polarizing plates are secured on both side of those two substrates, and light beams from these polarizing plates are used for a display shutter when displaying a color image.
In the liquid crystal display device using the plastic beads as a spacer, however, alignments of the liquid crystal peripheral to the spacer, which are scattered between the two substrates, are disordered, resulting in such a problem that the contrast declines due to a leakage of light beams from the spacer peripheral portion. Moreover, the spacers are hard to disperse uniformly and are arranged with ununiformity during a step of dispersing the spacers on the substrate. This results in a display defect, which in turn brings about a decreases in yield.
Under such circumstances, there is proposed a liquid crystal display device using no plastic beads, wherein a pillar-shaped spacer is disposed by stacking a plurality of color layers of color filters.
However, the sequence of forming those color layers is not necessarily fixed and, it may happen, changes depending on a situation in terms of manufacturing line or a lot. As a result, the following problems arise.
(1) In the case that pillar-shaped spacers of stacked a plurality of color layers are disposed on an opposite substrate, an alignment film is disposed on the surface of a switching elements such as TFT and TFD on an active matrix substrate to which the pillar-shaped spacers are disposed proximally. This alignment film is, however, as thin as approximately 1000 .ANG., and impurities contained in the respective color layers constituting the spacer penetrate enough to reach the TFT. The impurities causing problems are alkali metals and Chlorine (Cl) and Fluorine (F), and the TFT might cause a malfunction because of the impurities.
In this case, impurity content quantities and impurity elution quantities of the respective color layers are different, and hence, when the color layer containing a great deal of impurities comes to a highest layer positioned in the vicinity of the switching element such as the TFT and TFD, this leads to a deterioration in terms of characteristics of the switching element with a diffusion of the impurities into the switching element.
(2) If a hardness of each color layer is different, there might also differ a cut quantity due to rubbing when stuck to an opposite substrate, and therefore a desired gap can not be obtained.
(3) In the case of a multi-gap corresponding method of showing a correspondence to a plurality of gaps by changing a thickness of at least one colored film among thicknesses of a plurality of color layers, a spacer height changes as a stacked sequence varies, and it is impossible to correspond to a predetermined gap.
(4) If a surface roughness of each color layer is different, the predetermined gap can not be obtained because of a difference in strength of the stacked pillar, a difference in collapse quantity when stuck to the opposite substrate, and a difference in degree of contact with the opposite substrate when stuck thereto.